Deal officials say a cushion is needed because the state really isn’t sure about the federal law’s effect: The windfall from higher taxes could be much less or much more.

Georgia — and many other states — would receive a windfall because the federal law limits or eliminates some of the deductions Georgians have used when figuring their state taxes in the past and made it far more likely that ratepayers will use the standard federal deduction, rather than lowering their state taxable income using itemized deductions.

Currently, if Georgians take the standard deduction on their federal tax return, they must do the same on their state form. That is an issue in part because the state standard deduction — $3,000 for joint filing couples — is fairly low.

In addition, Deal’s bill would increase the state personal exemption by 25 percent.

During the first hearing on the bill Wednesday, House tax writers made it clear they want the windfall whacked further.

State Rep. Chuck Martin, R-Alpharetta, a member of the House Ways and Means Committee, said doing nothing would be “horrible” and mean a tax increase for many Georgians. If lawmakers pass Deal’s plan, he said, the impact would merely be “bad.”

But state Rep. Chuck Efstration, a Deal floor leader and sponsor of the bill, urged colleagues to consider the plan, noting that they could cut taxes further in the future.

“There will be an opportunity for greater tax relief, which we do not have if we do nothing,” said Efstration, a Republican from Dacula.

State income taxes are the single biggest source of revenue for the state, and officials in the Deal administration have indicated that the governor would likely fight any effort to cut the rate and veto any bill that contained rate cuts.

But lawmakers are squeamish about the prospects of running for re-election this year after passing a plan that doesn’t wipe out the windfall because they could be accused of raising state income taxes.